In 1956, Meagher graduated from Sydney University with degrees in Arts and Law. He was awarded university medals in History and Law. He attended St John's College and was House President there and, later, a member of its governing Council for many years.

Meagher was called to the NSW Bar in 1960. He lectured at the Faculty of Law at Sydney University within the same year. After taking Silk, Justice Meagher served as President of the New South Wales Bar Association from 1979 to 1981.

In 2000 the Senate of the University of Sydney conferred on Meagher—"scholar, lawyer, judge and individualist", as the citation to the Senate called him—the honorary degree of Doctor of Laws (LLD), a very rare distinction. The Senate was invited to confer the degree on Meagher for his intellectual contributions to the law in particular, referring to the classic text Equity: Doctrines & Remedies, of which Meagher was and remains co-author, as having helped reverse the general decline of equity jurisprudence: "[t]hat book has probably enjoyed greater esteem than any other Australian legal treatise, not only in universities but also with the Bench and Bar in this country, England and elsewhere. There is no equivalent to it in England, the United States or anywhere else".[3] The citation also commended Meagher's service to the University of Sydney Faculty of Law, in his capacity since 1960 as lecturer in Roman law and then Challis Lecturer in Equity, commenting that "[h]is lectures were a constant source of inspiration, delight and guidance for generations of law students".[2]

In 2005 Meagher was admitted as an Officer of the Order of Australia "for service to the judiciary, particularly judicial administration, to reform of the building and construction industry, and to the community through the Australian Naval Reserve and conservation and arts organisations Archived July 1, 2005 at the Wayback Machine.

When John Laws was fined $50,000 for using "gross and coarse" terms on 2UE, Justice Meagher dissented and called for a jail term, stating that $50,000 was the sort of money Laws would spend "on a small cocktail party."[4]

Justice Mary Gaudron, in a speech to the Women Lawyers Association of NSW, brought Meagher into controversy by deeming his comment that "The bar desperately needs more women barristers [because] there are so many bad ones that people may say that women ... are hopeless by nature"[5] as evidence of a brooding "wilfully unreconstructed" view of women in Law.

He notably opposed the move of Sydney UniversitySchool of Law from the City to Darlington campus, saying, "As long as it was in the city, the school had lots of barristers and solicitors prepared to lecture there, but those people will not be prepared to struggle up to the University. There has never been a close inter-relationship between the professions and the academics in law ... There's a certain amount of co-operation at the moment but even that amount is going to vanish"[6].